Fuse type initiator and booster system containing same



April 8, 1969 P. G. NEWMAN 3,437,037

FUSE TYPE INITIATOR AND BOOSTER SYSTEM CONTAINING SAME Filed Oct. 10, 1967 u Ilb I6 ll l4 b l2 FIG. 2A FIG. 2B

PHILIP G NEWMAN INVENTOR.

ATTORNEY nited States Patent Ofice 3,437,037 FUSE TYPE INITIATOR AND BOOSTER SYSTEM CONTAINING SAME Philip G. Newman, Kenvil, N.J., assignor to Hercules Incorporated, Wilmington, DeL, a corporation of Delaware Filed Oct. 10, 1967, Ser. No. 674,278 Int. Cl. F42b 1/04, 1/02, 3/10 US. Cl. 102-44 9 Claims ABSTRACT OF THE DISCLOSURE This invention relates to detonating fuse structure for booster assemblies. In one aspect this invention relates to booster assemblies containing detonating fuse structure providing for high core loadings without an accompanying increase in bulk and sacrifice of flexibility of the assembly. Other aspects of the invention will be apparent to one skilled in the art in light of the accompanying disclosure and the appended claims.

A complete explosive assembly ready for firing constitutes a main explosive charge with means for initiating same. One such assembly constitutes a combination of a main explosive charge such as a nitrocarbonitrate, with a booster assembly as a secondary initiator and an electric blasting cap or a detonating fuse as a primary initiator. The explosive charge in the booster assembly, i.e. the booster charge is detonated in response to actuation of the primary initiator and the main charge is detonated in response to the detonation of the booster charge to provide the full explosive force of the assembly.

One type of generally utilized primary initiator is a detonating fuse which is a strand, generally formed from plastic, containing a core of cap-sensitive high explosive at a suitable loading normally in the order of from 50 to 75 grains per foot. Primacord is one such Well-known fuse structure.

Often, however, higher core loadings are required, e.g. in the' order of 100 to 200 grains per foot. This has been disadvantageous due particularly to the accompanying loss in compactness of the booster assembly and the loss of flexibility of the tail portion extending from the booster to the energy source, due to the requisite increase in size of the fuse at the higher core loadings.

This invention is concerned with detonating fuse structure, and with a booster assembly containing same, to provide higher than normal core loadings without incurring appreciable loss in compactness of the booster assembly, while at the same time providing increased flexibility of the tail portion extending from the booster to the energy source.

In accordance with the invention, a detonating fuse system for a booster assembly is provided which comprises a detonating fuse element disposed as a U-shape loop and having a core loading of at least 50 grains PETN (or equivalent) per foot; a separate detonating fuse, as a tail member for said system, having a core loading not exceeding 40 grains PETN (or equivalent) per foot and extending in direct contact with said fuse element from within said loop through the open end 3,437,037 Patented Apr. 8, 1969 thereof, and then to a point outside said loop; and means for supporting said tail fuse and said fuse element in said direct contact.

Also in accordance with the invention, a booster assembly containing a booster charge and the above described detonating fuse system, as the initiator therefor, is provided.

The invention, in providing a detonating fuse system containing a high core loading in the initiation zone, and a low core loading in the tail member provides high detonating strength while eliminating undue bulk, and sacrifice in flexibility, inherent in the use of conventional high core loaded detonating fuse initiators of comparable initiating strength.

The invention is illustrated with reference to the drawings of which FIGURE 1A is a view of a detonating fuse system of the invention showing a combination of two separate strands of detonating fuse as the detonating fuse element, and FIGURE 1B is a view the same as that of FIGURE 1A except that it is turned to the left; FIG- URE 2A is a view of a detonating system similar to that of FIGURES 1A and 1B except that the detonating fuse element is formed from a single strand of detonating fuse, and FIGURE 2B is a view taken along the line 2B-2B of FIGURE 2A; and FIGURE 3 is a view of a now-preferred booster assembly of the invention comprising a high explosive charge, for example cast pentolite, in combination with a detonating fuse system of the invention.

Referring to FIGURE 1A, separate detonating fuse strands 11a and 11b, in detonating fuse system 10 extend in parallel in close proximity to, and generally, in direct contact with, the other as a dual strand along the path of a U-shape loop to form a resulting detonating fuse element 11 having a core loading of at least 50 grains PETN (or equivalent) per foot. Generally, the core loading of the U-shape fuse element 11 is in the order of from about 50 to 300, more often from about to 200, grains PETN (or equivalent) per foot.

A separate detonating fuse 12, as a tail fuse for the detonating fuse system 10, has a core loading not exceeding 40 generally from 5 to 35 and preferably 15 to 30 grains PETN (or equivalent) per foot and extends in contract with :fuse element 11 from within the U-loop through the open end of the loop, and then to an outside point, i.e. a point external to the loop. As further illustrated with reference to FIGURE 1B, and in accordance with preferred practice, detonating fuse 12 extends inside the loop from direct contact with substantially the closed end thereof, through the open end 13 along, and in direct contact with, at least one of the strands 11a or 11b, so as to thereby be in direct contact with the fuse element 11.

Detonating fuse 12 is supported in the loop of fuse element 11 in direct contact with fuse element 11 by any suitable means, such as by a metal tie 14 disposed around a section of fuse element 11 through which fuse 12 ex ten-ds. Although a tape, ring member, cord, or the like, can be utilized as a support member 14 in lieu of a metal tie, the metal tie is prefer-red inasmuch as it not only adequately maintains the necessary contact of the two detonating fuse members, but it is particularly advantageous from the standpoint of additional detonating energy that results at the time of initiation from the formation of molten metal particles and impact of same with the booster charge.

Referring to FIGURE 2A, wherein primed numbers refer to like parts of FIGURE 1A identified by the same but unprimed numbers, a single strand detonating fuse 16 extends along the path of a U-shape loop to form a detonating fuse element 17 which is the same as fuse element 11 of FIGURES 1A and 1B except that it (element 17) is formed from the single fuse strand. The core loading of fuse element 17, and hence its length measured along its longitudinal axis, can be the same as, or different from that of fuse element 11 of FIGURE 1A, dependent on the particular booster assembly requirements. However, the core loading of element 17 is at all times within the range of that described with reference to fuse element 11, viz. at least 50 and generally from 50 to 300*, but more often from 100 to 200 grains PETN (or equivalent) per foot.

A separate detonating tail fuse 12', of the same core loading as that of detonating fuse 1 2 of FIGURE 1A extends from within the loop of fuse element 17 through the open end thereof in contact with fuse element 17, preferably from contact with substantially the closed end of element 17. This is more specifically illustrated with reference to FIGURE 2B.

Detonating fuse 12' is supported in the loop of detonating fuse element 17 in contact with fuse element 17 in any suitable manner such as by a metal tie 14' around a section of fuse element 17 through which detonating fuse 12' extends, as illustrated with reference to tie 14 fuse element 11, and detonating fuse 12 of FIGURE 1A.

The invention as illustrated with reference to the drawings provides for a high core loading in the initiation zone to provide a resulting booster assembly of high detonating strength without incurring the economic necessity of running the conventional high core loaded fuse all the way to the energy source; and it also provides for a tail fuse cross-section sufliciently small that the tail fuse is flexible and can thereby be easily handled for tying into the energy source often a fuse trunkline. Further, due to the concentrated core loading and accompanying tail fuse of high flexibility, the detonating fuse system, as an element of a booster assembly, can be easily packed into a small space for storage, shipping and routine handling.

The detonating fuse system of the invention can be fabricated in any suitable manner. In a now preferred embodiment the detonating fuse element is a double strand such as illustrated with reference to element 11 of FIG- URE 1. Although the double strand fuse element can be constructed in any suitable manner, it can advantageously be formed from a dual strand fuse material commercially available, as Primacord manufactured by Ensign- Bickford Company.

In either of the embodiments of the fuse system of the invention the detonating fuse, for the formation of the fuse element, is cut at its predetermined length which, in turn, depends upon the particular need at hand, and then shaped in U form; and the tail detonating fuse is inserted into position in the U. The tie is then applied around a section of the resulting U shape detonating fuse element, through which the tail fuse extends, for the necessary support of contact of the two fuse members as illustrated hereinabove. Thus, for example, if a tail fuse, say fuse 12 of FIGURE 1A, having a core loading of 25 grains per foot, is utilized in combination with a dual strand-type detonating fuse having a core loading of 100 grains per foot, such as fuse element 11 of FIG- URES 1A and 1B (50 grains for each strand 11a and 11b) and it is required that a total of 20 grains of high explosive be available for the initiation, the length of each strand 11a and 11b (each of the same length) will necessarily be about two inches and hence the length of the entire fuse element 11 will be in the order of one inch as measured along the longitudinal axis of its loop. Generally, dependent upon the choice of core loadings for the tail detonating fuse and the detonating fuse element of the detonating fuse system of the invention, the length of the detonating fuse element and tail fuse portion therein will be in the range of /2 to 6 inches, more often from to about 3 inches. The tail fuse portion extending from the fuse element will be of any suitable length dependent upon that required for connection with the particular energy source therefor. The core loadings of the fuse element and tail fuse members of the detonating fuse system of the invention are generally in the order of from 50 to 300 (preferably to 200) and 5 to 35 (preferably 15 to 30), respectively, grains PETN (or equivalent) pe foot, as above described in more detail.

Referring to FIGURE 3, wherein primed index numbers refer to like parts shown in FIGURE 1 identified therein by the same 'but unprimed numbers, booster initiator assembly 21 comprises booster charge 22 containing a detonating fuse system of FIGURE 1A as the nowpreferred initiator therefor. Charge 22 is any suitable booster charge type high explosive such as PETN, pentolite, tetryl, composition B, or the like, substantially filling closed shell 19. In preferred practice charge 22 is a cast high explosive such as composition B or pentolite. Detonating fuse system 10", supported in any suitable manner, in shell 21is disposed within charge 22 with element 11' in detonating relationship with charge 22, and with tail fuse member 12" extending from charge 22 through shell 21 to a suitable energy source outside shell 21. Thus, upon extension of the tail fuse 12 to its energy source (not shown) such as a trunk fuse line, detonating fuse element 11' is fired to cause detonation of booster charge 22, which in turn causes detonation of the main explosive charge of the complete explosive assembly (not shown).

By way of further illustration, 25 primer assemblies of FIGURE 3 were assembled and fired, as summarized in the following tabulation:

Booster charge: Cast Pentolite Grams 80. Shape Cylindrical, 1

inch length by 1% inches diameter. Detonating fuse system: PETN loaded U-shape element (double strand) Core loading 100 grains per foot.

Each strand 50 grains per foot.

Length 1 inch. Tail fuse:

Core loading 25 grains per foot.

Length beyond U fuse element 1 /2 feet.

In each instance the tail fuse was flexible and easily tied by a single square knot to the energy source which was then initiated with accompanying initiation of the fuse system and detonation of the booster charge. All 25 shots of the pentolite charge were complete.

In general practice, both sides of the detonating fuse element and the individual strands of the double strand fuse element, are of substantially the same length; and both strands of the double strand fuse element are of substantially the same core loading. However, when desired, the lengths of the sides of the fuse element and of double strands forming the fuse element, and the core loadings of the individual strands forming the double strand fuse element need not be the same.

A tra-y method for the manufacture of booster assemblies containing a detonating fuse system of the invention in conjunction with cast booster charges, and resulting product, are disclosed and claimed in my US. application, Ser. No. 674,337 filed concurrently herewith.

What I claim and desire to protect by Letters Patent is:

1. A detonating fuse system which comprises a detonating fuse element disposed as a U-shaped loop having a core loading of at least 50 grains PETN (or equivalent) per foot; a separate detonating fuse, as a tail member for said system, having a core loading not exceeding 40 grains PETN -(or equivalent) per foot and extending in direct contact with said fuse element from within said loop along the length of said loop and through the open end thereof; and means for supporting said tail fuse and said fuse element in said direct contact.

2. A detonating fuse system of claim 1 wherein the core loading of said detonating fuse element is in the range of from 50 to 300 grains per foot; and wherein the core loading of .said tail fuse member is within the range of from 5 to 35 grains per foot.

3. A detonating fuse system of claim 2 wherein the core loading of said detonating fuse element is in the range of from 100 to 200 grains per foot and the core loading of said tail fuse is in the order of from 15 to 30 grains per foot.

4. A detonating fuse system of claim 3 wherein said fuse element is formed from a double strand of detonating fuse.

5. A detonating fuse system of claim 1 wherein said fuse element is formed from a double strand of detonating fuse.

6. A detonating fuse system of claim 1 wherein said detonating fuse element is formed from a single strand of detonating fuse.

7. A detonating fuse system of claim 1 wherein said means for supporting said tail fuse and said detonating fuse element in said contact is a metal tie disposed around a portion of said detonating fuse element through which a portion of said tail fuse extends.

8. A detonating fuse system of claim 2 wherein the length of said loop, measured along its longitudinal axis, is within the range of from A: to 6 inches.

9. A booster assembly comprising a booster type high explosive charge, and as an initiator therefor, a detonating fuse system comprising (1) a detonating fuse element disposed as a U-shape loop having a core loading of at least 50 grains PETN (or equivalent) per foot (2) a separate detonating fuse, as a tail member for said system, having a core loading not exceeding 40 grains PETN (or equivalent) per foot and extending in direct contact with said fuse element from within said loop along the length of said loop and through the open end thereof and (3) means for supporting said tail fuse and said fuse element in said direct contact; said detonating fuse element being disposed within said high explosive, and said tail fuse extending from said detonating fuse element to a point external to said high explosive charge.

References Cited UNITED STATES PATENTS 3,037,453 6/1962 Cook et a1. 102-24 3,288,065 11/ 1962 Tousley 10224 FOREIGN PATENTS 599,612 6/1960 Canada. 599,614 6/1960 Canada. 663,864 5/ 1963 Canada.

VERLIN R. PENDEGRASS, Primary Examiner.

US. Cl. X.R. 102-27 

